The networking configuration does not allow the EC2 instances to reach the internet via a NAT gateway or internet gateway, preventing access to the CodeDeploy endpoint.

The IAM user initiating the deployment lacks the necessary permissions to interact with the CodeDeploy service.

The target EC2 instances are not correctly registered with the CodeDeploy service.

The EC2 instances do not have an attached IAM instance profile with the required permissions for CodeDeploy.

The application revision does not include the necessary appspec.yml file.